Ignore clippy::redundant_guards warning

```
error: redundant guard
  --> tools/codegen/src/main.rs:91:24
   |
91 |                     if matches!(vis, syn::Visibility::Public(..)) =>
   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_guards
   = note: `-D clippy::redundant-guards` implied by `-D warnings`
help: try
   |
90 -                 syn::Item::Struct(syn::ItemStruct { vis, ident, fields, .. })
90 +                 syn::Item::Struct(syn::ItemStruct { vis: syn::Visibility::Public(..), ident, fields, .. }) =>
   |
```

tools/codegen/src/main.rs

@@ -1,5 +1,5 @@
 #![warn(rust_2018_idioms, single_use_lifetimes)]
-#![allow(clippy::match_on_vec_items, clippy::needless_pass_by_value)]
+#![allow(clippy::match_on_vec_items, clippy::needless_pass_by_value, clippy::redundant_guards)]
 
 #[macro_use]
 mod file;